The ovalbumen (the principal protein in egg whites) degrades with time, as does any protein for that matter. They won't be able to give you the results you need, which is beside the point that doing anything other than making a trip to the dumpster with month-old egg whites is frankly alarming.

For the purposes of making macarons, I would start with new egg whites. However, as long as these smell ok and there does not appear to be anything growing in them, I agree with Monita that consumption after sufficient heating sounds reasonable. In food safety terms, eggs keep forever in the fridge (even while certain preparation-specific but food-safety-unrelated aspects degrade/improve) so it really just depends how clean the container is and how clean your hands were when you separated them. Omelette sounds delish & good luck w the macarons!

Eggs in the shell (properly handled and stored) are good up to 80 days from packing. Once deprived of their protective layer, the USDA recommends using them within 4-5 days. That's "days" not "weeks"...

Well, USDA also advises against eating raw eggs and a lot of other things people, including myself, do all the time (and maybe some egg lobby is paying off USDA, who knows). My rule of thumb for home cooking -- not in places where HACCP applies/Health Dept comes to do inspections, or private cheffing, as the case may be -- is that if it doesn't smell bad or look like something is growing in it, then if it tastes ok it is ok. I use this across the board, whether it's for brewing, fermenting, the bowl of pesto in my fridge that was fine after a month, what have you; following USDA guidelines religiously with a magnifying glass is often wasteful as they err extremely (/luxuriously) on the side of caution (how many people on the planet would take those eggs right now?). So, Peter, if they smell ok, it may not be the best omelet ever but I think it would be tasty enough if you decide to make it :)

I've read that Pierre Herme ages his egg whites for macarons at room temp for a couple days, so yours being in the fridge should be good to go. Properly stored they should be safe, and if they whip up properly, it seems like there shouldn't be an issue. Enough weasel words in there for you? ;)